Cooling control circuit for peltier device

ABSTRACT

A cooling control circuit for a Peltier device comprises: a switching device  3 ; an LC filter  4, 13  connecting between the switching device  3  and the Peltier device  1 , the LC filter  4, 13  smoothing an output from the switching device  3;  an amplifier circuit  6  amplifying an output from the LC filter  4, 13 ; and a switching device control circuit IC configured to control an on-state and off-state of the switching device  3  based on a level of an output from the amplifier circuit  6 . The amplifier circuit  6  delays and amplifies the output from the LC filter  4, 13  so that a maximum level of the output from the LC filter  4, 13  reaches a level at which the switching device control circuit IC brings a switching device  3  into the off-state.

TECHNICAL FIELD

The present invention relates to a cooling control circuit for a Peltier device.

BACKGROUND ART

A patent document 1 discloses a technique to produce condensed water from moisture of the air by a cooling control of a Peltier device.

In the foregoing technique of the patent document 1, the Peltier device cools a discharge electrode to generate condensed water thereon from moisture of the air. A high voltage is applied to the condensed water via the discharge electrode, thereby charged water fine particles are generated by an electrostatic atomization of the condensed water. The charged water fine particles include radicals, and the typical sizes are a few to tens of nanometers. The charged water fine particles are sometimes called as fine water droplets or nano-sized mist.

CITATION LIST Patent Literature

The Japanese Patent Application Laid-Open Publication No. 2006-26629

SUMMARY OF INVENTION Technical Problem

In the forgoing technique, a step-down chopper (buck chopper) circuit is used as a control circuit for cooling the Peltier device. The step-down chopper circuit outputs a voltage to cool the Peltier device by an oscillation of a switching device (e.g. Field Effect Transistor) therein. However, the switching device oscillates continuously, and thereby outputs the voltage having a waveform as shown in FIG. 3. Therefore, when a switching frequency of the switching device becomes higher, a power is more continuously supplied to the Peltier device, and thus a rising rate of temperature of the Peltier device will increase.

In addition, when a switching speed increases for reduction of the rising rate of temperature, noise components in the output voltage from the step-down chopper circuit will increase and this may be a problem.

The present invention has been made with consideration of the above situation, and the object is to provide a cooling control circuit of a Peltier device capable of reducing a rising rate of temperature of the Peltier device and of reducing noises in an output voltage to the Peltier device.

Solution to Problem

An aspect of the present invention is a cooling control circuit for a Peltier device comprising: a switching device; an LC filter connecting between the switching device and the Peltier device, the LC filter smoothing an output from the switching device; an amplifier circuit amplifying an output from the LC filter; and a switching device control circuit configured to control an on-state and off-state of the switching device based on a level of an output from the amplifier circuit. The amplifier circuit delays and amplifies the output from the LC filter so that a maximum level of the output from the LC filter reaches a level at which the switching device control circuit brings a switching device into the off-state.

Advantageous Effects of Invention

It is possible to provide a cooling control circuit for a Peltier device having a simple configuration, which can reduce a rising rate of temperature of the Peltier device and can reduce noises in an output voltage to the Peltier device in the cooling thereof.

BRIEF DESCRIPTION OF DRAWINGS

[FIG.1]FIG. 1 is a schematic circuit diagram showing a cooling control circuit for a Peltier device according to an embodiment of the present invention.

[FIG. 2]FIG. 2 shows a waveform of an intermittent oscillation generated in the cooling control circuit shown in FIG. 1.

[FIG. 3]FIG. 3 shows a waveform of a continuous oscillation generated in a conventional cooling control circuit.

[FIG. 4]FIG. 4 is a schematic diagram showing a configuration of an electrostatic atomizer using a cooling control circuit for a Peltier device according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

An embodiment according to the present invention is described hereinafter with reference to figures.

FIG. 4 is a schematic diagram showing a configuration of an electrostatic atomizer using a cooling control circuit 10 of a Peltier device 1 according to the embodiment of present invention. In the present embodiment, the Peltier device 1 has: a pair of a P-channel semiconductor 1 a and an N-channel semiconductor 1 b; a connecting portion 1 c electrically connected with the cold sides of the P-channel and N-type semi-conductors 1 a and 1 b; electrically conductive members 1 d and 1 d for heat radiation, which are made of electrically conductive material and are connected with the hot sides of the P-channel and N-type semiconductors 1 a and 1 b, respectively; and lead wires 1 e and 1 e connected with the electrically conductive members 1 d and 1 d.

In the embodiment as shown in FIG. 4, a discharge electrode 7 is provided the connecting portion 1 c in a protruding manner.

In the electrostatic atomizer, a case 8 is provided. The case 8 is made of electrically insulating material and is formed into a tubular shape having a bottom wall 8 a at an end thereof. In the bottom wall 8 a, a through hole 8 b is formed. The electrically conductive members 1 d and 1 d are inserted into the through hole 8 b and fixed to the case 8. Accordingly, the discharge electrode 7 is accommodated in the case 8.

The case 8 has an opening portion at another end opposite to the end at which the bottom wall 8 a is provided. At the opening portion, an electrode 9 is supported so as to face to the discharge electrode 7. The electrode 9 is formed into a ring shape having a discharge hole 12 at the center thereof. The electrode 9 is grounded.

Each lead wire 1 e is electrically connected to an electric wire. The electric wire is connected to the cooling control circuit 10. The cooling control circuit 10 includes a power supply (not shown). In the embodiment as shown in FIG. 4, a high voltage supplier 11 is connected to the electric wire. The high voltage supplier 11 applies a high voltage to the discharge electrode 7.

The cooling control circuit 10 has a switching power supply circuit (switching power supply) 2 as described later. A cooling control of the Peltier device 1 is carried out by an output from the switching power supply circuit 2. In this cooling control, the connecting portion 1 c is cooled and thereby the discharge electrode 7 projecting from the connecting portion 1 c is also cooled. When the discharge electrode 7 is cooled, moisture of the air is condensed on the discharge electrode 7 as condensed water. Specifically, cooling of the discharge electrode 7 supplies water thereto. Alternatively, heat generated in the cooling is radiated from the electrically conductive members 1 d and 1 d.

When the high voltage supplier 11 applies a high voltage to the discharge electrode 7 while the condensed water adheres on the discharge electrode 7, an electrostatic atomization of the condensed water is generated. In the electrostatic atomization, large amount of charged water fine particles is produced. As described already, the charged water fine particles include radicals, and the typical sizes are a few to tens of nanometers. The charged water fine particles are sometimes called as fine water droplets or nano-sized mist.

FIG. 1 shows an exemplary configuration of the switching power supply circuit 2 which is configured as a step-down chopper (buck chopper) circuit. The switching power supply circuit 2 has: a switching device 3; inductor 13; a smoothing capacitor (hereinafter referred to as capacitor) 4 on the output side; diode 14; amplifier circuit 6; switching device control circuit (switching device controller) IC. In FIG. 1, the reference numbers 16 and 17 indicate capacitors.

In the present embodiment, the switching device 3 is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). A gate terminal of the switching device 3 is connected to the switching device control circuit IC through a resistor R4, and the switching device 3 receives a PWM (Pulse Width Modulation) control signal therefrom. The switching device 3 is in an on-state when the PWM control signal is in a low-state, and it is in an off-state when the PWM control signal is in a high-state.

As shown in FIG. 1, a source terminal of the switching device 3 is connected to a power supply (not shown), and a drain terminal thereof is connected to an LC filter including the inductor 13 and capacitor 4. Specifically, the drain terminal is connected to a positive terminal of the capacitor 4 through the inductor 13.

Both terminals of the capacitor 4 are connected to the Peltier device 1. An output from the switching device 3 is smoothed by the LC filter, sent to the Peltier device 1, and thereby the Peltier device 1 is cooled.

The amplifier circuit (amplifier) 6 amplifies and a voltage or current from the LC filter and outputs it to the switching device control circuit IC. In the present embodiment, the amplifier circuit 6 is a non-inverting amplify circuit including: an operational amplifier OP; and two resistors R1 and R2 that determines a gain (amplification factor) of the amplifier circuit 6. The resistor R1 is connected between an inverting input terminal and an output terminal of the operational amplifier OP. The resistor R2 is connected between the inverting input terminal of the operational amplifier and the ground. A non-inverting input terminal of the operation amplifier OP is connected to the positive terminal of the capacitor 4 through a resistor R3. An output from the operational amplifier OP is received by the switching device control circuit IC.

The amplifier circuit 6 delays the output from the LC filter by a response lag (delay) characteristics of the operational amplifier OP. In addition, the gain of the amplifier circuit 6 is set to a value at which the switching device control circuit IC brings the switching device into the off state. The gain is about 120 or 20 when the amplifier circuit is a current-voltage amplifier or voltage-voltage amplifier, respectively. However the gain is set depending on electric characteristics of the Peltier device 1, the inductor 13, capacitor 4, for example. Therefore, the present invention is not limited to these values as described above.

Based on the output from the amplifier circuit 6 as described above, the switching device control circuit IC oscillates intermittently the switching device 3 (the detail is described later).

The switching device control circuit IC outputs the PWM control signal to the switching device 3 to control the on-state and the off-state thereof. Whether the PWM control signal comes into the on-state or the off-state depends on a level of the output from the amplify circuit 6, which the switching device control circuit IC receives. Specifically, while the level is lower than a predetermined threshold level (e.g. a threshold voltage), the PWM control signal is in the low-state, and thereby the switching device 3 is brought into the on-state. Alternatively, while the level is higher than the predetermined threshold level, the PWM control signal is in the high-state, and thereby the switching device 3 is brought into the off-state.

The switching device control circuit IC may include an oscillator (not shown) which generates an oscillation signal having a predetermined frequency. In this case, when the switching device control circuit IC receives an output from the LC filter as a feedback signal without passing through the amplify circuit 6, the switching device control circuit IC outputs a PWM control signal having a duty ration based on the received the output level. That is, the switching device control circuit IC monitors the output from the LC filter in real time.

However, a switching frequency in the present embodiment does not depend on a frequency of the foregoing oscillator. In the present embodiment, since the switching device control circuit IC receives an output from the LC filter through the amplify circuit 6, the output of the amplify circuit 6 changes with a delay with respect to a change of the output of the LC filter due to the response delay characteristics of the amplify circuit 6. Accordingly, even when the switching device 3 comes into an on-state by a low-state of the PWM control signal, an output from the switching device control circuit IC does not immediately increase. Consequently, the switching device control circuit IC maintains the low-state of the PWM control signal, and thereby the on-state of the switching device 3 is extended. Thereafter, the output from the amplify circuit 6 increases and reaches a threshold level at which the state of PWM control signal is switched from the low-state to a high-state. At this time, the switching device control circuit IC switches the PWM control signal into a high-state. Accordingly, the switching device 3 is switched into an off-state, and an output from the LC filter starts to decrease. However, even when the output of the LC filter starts to decrease, the output of the amplify circuit 6 continues to increase due to the response delay characteristics. Thereafter, the output of the LC filter decreases, but the level thereof remains to be higher than the threshold level resulting from amplification of the amplify circuit 6. Therefore, the switching device control circuit IC maintains the high-state of the PWM control signal for a while. The output of the LC filter further decreases, and the output of the amplify circuit 6 reaches a level lower than the threshold level. As the result, the switching device control circuit IC switches the PWM control signal into the low-state again, thereby brings the switching device 3 into the on-state.

With the above configuration, the switching device 3 oscillates intermittently. In this case, a waveform at a point V in FIG. 1 is like that shown in FIG. 2. For example, a switching frequency and a duty ratio thereof are 40 to 60 kHz and 10 to 20 percents, respectively. It should be noted that the present invention is not limited to the above values.

On the other hand, when the output from the LC filter is fed back to the switching device control circuit IC without passing through the amplify circuit 6, the switching device 3 oscillates continuously, and a waveform at the point V is like that shown in FIG. 3. Meanwhile, in this case, the switching device control circuit IC includes the oscillator as described above, and a frequency and a duty ratio of the waveform of FIG. 3 are 300 kHz and 10 to 20 percents, respectively, for example.

According to the present embodiment, it is possible to intermittently oscillate the switching device 3. Therefore, compared with the continuous oscillation in a conventional cooling control circuit without the amplify circuit 6, it is possible to reduce the switching frequency with the same duty ratio. Consequently, increase of temperature of a Peltier device can be reduced.

Further, since the increase of the temperature, it is possible to reduce the switching speed and occurrence of noises.

In the circuit of FIG. 1 according to the present embodiment, the output voltage at the LC filter (capacitor 4) is fed back to the switching device control circuit IC through the amplify circuit 6. However, an output current from the LC filter (capacitor 4) may be fed back to the switching device control circuit IC through the amplify circuit 6. In both cases, it is possible to intermittently oscillate the switching device 3 utilizing the response delay characteristics of the amplify circuit 6.

It should be noted that the Peltier device 1 is not limited to the configuration as shown in FIG. 4. Specifically, plural pairs of a P-channel semiconductor 1 a and a N-channel semiconductor 1 b may be arranged and connected in series.

The connecting portion 1 c and discharge electrode 7 may be formed separately to each other, and an end portion of the discharge electrode 7 may be fixed to the connecting portion 1 c.

In the electrostatic atomizer according to the present embodiment, the electrode 9 may be omitted. 

1. A cooling control circuit for a Peltier device comprising: a switching device; an LC filter connecting between the switching device and the Peltier device, the LC filter smoothing an output from the switching device; an amplifier circuit amplifying an output from the LC filter; and a switching device control circuit configured to control an on-state and off-state of the switching device based on a level of an output from the amplifier circuit; wherein the amplifier circuit delays and amplifies the output from the LC filter so that a maximum level of the output from the LC filter reaches a level at which the switching device control circuit brings a switching device into the off-state. 